1. Field of the Invention
This invention relates to cathodes, and particularly to cathode-heater assemblies and a rugged vibration resistive support structure therefor.
2. Description of the Prior Art
The prior art related to this invention is believed found in Class 313, sub-classes 271 and 337 and includes United States patents cited in prior U.S. Pat. Nos. 3,906,276 and 3,914,639.
It is one of the important objects of the present invention to provide a cathode-heater assembly in which the cathode is supported directly by the heater.
It is another object of the present invention to provide a cathode-heater assembly associated with a mounting or support structure therefor that requires significantly lower power than conventional cathode-heater assemblies to achieve satisfactory electron emission levels.
Another object of the invention is the provision of a cathode-heater assembly that utilizes a mounting structure that resists displacement of the cathode-heater assembly in all directions.
Cathode-heater assemblies of conventional types have been deficient in that considerable power is required to bring the cathode temperature to an electron emissive level. Conventional cathode assemblies utilizing, for instance, a 1/8" diameter cathode such as used in a cathode ray tube (CRT) require approximately thirty seconds to achieve satisfactory operating temperature. Accordingly, it is another object of this invention to provide a cathode-heater assembly that achieves satisfactory operating temperature in from seven to ten seconds.
It is well known that conventional CRT cathodes of approximately 1/8" diameter having an oxide emissive layer require power at a level of about 50 watts per square centimeter to raise the temperature of the cathode to about 850.degree. C., this temperature providing a satisfactory level of electron emission. Accordingly, a still further object of the invention is to provide a cathode-heater assembly including a support structure therefor that requires a power level of only approximately 10 watts per square centimeter to bring the cathode to satisfactory electron emission temperature.
Indirectly heated cathodes are conventionally supported by a sleeve attached to the underside of the cathode button or to its cylindrical periphery, or the cathode is formed as the bottom part of a cup-shaped structure which tends to form a heat sink, thus drawing heat from the cathode button and therefore requiring the input of additional energy to compensate for the heat lost by conduction through the support structure. Accordingly, it is a still further object of the present invention to provide a cathode support structure which minimizes the loss of heat by conduction through the support structure.
In conventional cathode-heater assemblies, it is not unusual for the heater to operate approximately 400.degree. C. higher than the cathode temperature to compensate for the heat lost through conduction through the structure by which the cathode button is supported. It is therefore an object of the present invention to provide a cathode-heater assembly in which the differential of temperature between the cathode button and the heater is minimized to the point where these two temperatures are approximately the same.
One of the well known deficiencies of CRT cathodes is that the heater operates at a much greater temperature than the cathode. The heater is thus short-lived, prematurely destroying the entire assembly. Accordingly, it is a still further object of this invention to greatly increase the expected life of a cathode-heater assembly by providing a cooperative relationship between cathode and heater in which there is not such a great disparity in temperature between the heater and cathode.
Structurally, conventional CRT cathodes, whether of the dispenser type or of the oxide type, have been susceptible to impact shocks and vibration when used in environments in which such conditions are inherent. Such environments include weaponry and satellites and a host of other environments in which high impact shocks and vibration are present. In some instances, the structural arrangement between the cathode-heater assembly and the supporting structure for such assembly has not been designed to withstand such vibration, with the result that such assemblies are short lived. On the other hand, preferably ruggedized assemblies have had the disadvantage of conducting heat away from the cathode, thus requiring high power input. Accordingly, a still further object of the present invention is to provide a cathode-heater assembly supported in such a way that displacement in all directions is resisted by the structure so as to maintain the cathode in a fixed position, while the support structure functions as a heat dam rather than a heat sink, thus also reducing power requirements while increasing ruggedness.
Cathode-heater assemblies of conventional design are usually designed in a cylindrical configuration because in most instances the cathode button itself is circular. Such design configuration requires complex manufacturing techniques. We have found that a planar configuration is more expeditious from a manufacturing point of view, thus reducing the manufacturing cost for a given cathode-heater assembly and therefore making the cathode-heater assembly available at a more competitive price to a greater portion of the market. Accordingly, still another object of the invention is to provide a support structure for a cathode-heater assembly that is fabricated with reference to a planar configuration rather than a cylindrical configuration and which is susceptible to mass production techniques.
One of the difficulties encountered in the manufacture of a conventional cathode-heater assembly is the accurate placement of the cathode in relation to its supporting structure and in relation to the heater. Highly sopisticated equipment to achieve such placement has been required. Further, because of the small size of the units in question, each of the cathode buttons usually has to be individually handled and appropriately spot-welded to its supporting structure, which is usually independent of the heater and its support structure. Accordingly, a still further object is the provision of a cathode-heater assembly that constitutes a composite unit supported on integrally associated support structure common to both the cathode and the heater.
In conventional cathode-heater assemblies it sometimes happens that diode current emission occurs between the cathode and associated structure because of the close spacings required in extremely small assemblies. One of the objects of the present invention is to provide a cathode-heater assembly in which shield means are provided to eliminate, or reduce to an acceptable level, any such diode current emission.
It is well known by those skilled in the art that in many applications it is only a relatively small central area of a cathode that is the effective source of electrons. In many instances, merely to facilitate handling, the cathode button is much larger in diameter than the effective central emissive area of the cathode, thus increasing the mass of the cathode beyond what is needed for emissive purposes. Such excessive mass requires the input of greater heater power than would be required if the diameter of the cathode and therefore the mass could be reduced to approximately the effective diameter of the emissive area. Accordingly, it is still another object of the invention to provide a cathode-heater and support structure therefor that facilitates reduction of the cathode button diameter.
The invention possesses other objects and features of advantage, some of which, with the foregoing will be apparent from the following description and the drawings. It is to be understood however that the invention is not limited to the embodiment illustrated and described since it may be embodied in various forms within the scope of the appended claims.